The present invention generally relates to horn loudspeaker systems and more particularly to manifolds for coupling one or more acoustic drivers to a loudspeaker horn. The invention still further relates to improvements in the horn and horn manifold of a horn loudspeaker system which improve the directional characteristics of the loudspeaker without introducing significant distortion. The invention is particularly useful in arraying horn loudspeaker systems to achieve desired coverage while avoiding undesirable interactions between the horns.
To optimize a horn speaker system array, it is often desirable to control the dispersion characteristics of the horn such that the dispersion is narrow in the direction of the array and wide in the direction perpendicular to the array. Thus, in the case of a vertical stack of horn loudspeakers, destructive interaction between the acoustic output from the individual horns is minimized by controlling vertical dispersion. At the same time broad horizontal coverage is maintained for achieving desired audience coverage.
The existing approaches to horn loudspeaker design involve coupling the output of an acoustic driver to the throat end of a horn wherein the dispersion characteristics of the horn are governed by the horn design itself. Improved horn designs have been devised to achieve improved control over the directivity of a horn over a broad range of frequencies. Such a loudspeaker horn is disclosed in U.S. Pat. No. 5,925,856 issued to John D. Meyer et al., wherein a loudspeaker horn is provided with a special rectangular throat geometry and pre-load chamber for achieving uniform frequency response and coverage characteristics with low distortion. Such designs, however, are limited in their ability to achieve a suitably narrow dispersion that would permit an optimal array of the horns.
Another prior art approach to coupling drivers to a loudspeaker horn is disclosed in U.S. Pat. No. 4,629,029 issued to David W. Gunness. This patent discloses a manifold for connecting multiple drivers to the throat end of a horn so as to increase the acoustic power delivered by the horn. Again, such arrangements are limited by the horn""s directional control properties. Generally, highly directional horns can be achieved with long, slow, expanding horns, but even here the dispersion of the horn has a practical upper limit of about 20 degrees. Such long horn lengths are undesirable since distortion produced by the horn increases by the number of wavelengths over which the sound pressure waves are confined in the horn.
The present invention overcomes the inherent limitations of existing loudspeaker horn designs by providing a loudspeaker system and a manifold for a loudspeaker system which greatly improves the designer""s ability to control the dispersion characteristics of the horn. More specifically, the present invention provides a horn loudspeaker system and horn manifold which permits a horn to be driven by one or more acoustic drivers in a manner which achieves a narrow dispersion characteristic in one direction and a wide dispersion characteristic in the other to permit the loudspeakers to be arrayed easily without destructive interaction between their acoustic outputs.
The invention involves a horn loudspeaker system wherein one or more acoustic drivers are coupled to the throat end of a horn having an elongated throat opening. At least one acoustic driver of a loudspeaker system is coupled to the horn""s elongated throat opening by means of a manifold having an input end with at least one input port and an output end with at least two and suitably multiple aligned output ports. The aligned output ports of the manifold are connected to the input port by separate acoustic power waveguides. The acoustic power introduced to the input port of the manifold is divided between and passes through these waveguides so as to emerge from the manifold output ports as a virtual line array of acoustic power sources which are presented to the elongated throat opening of the horn. The manifold waveguides preferably have approximately equal acoustic path lengths such that the acoustical waves of the acoustic power divided between the waveguides arrives approximately in phase at the aligned output ports of the manifold.
For a horn whose elongated throat opening is oriented vertically, the manifold provides a vertical line array of output ports to simulate a vertical column of individual acoustic power sources in the throat of the horn. These individual acoustic power sources interact in accordance with well-known line array theory to control vertical dispersion from the line array. Thus, the vertical dispersion characteristics of the horn connected to the manifold are mainly governed by the line array characteristics of the horn""s elongated throat opening instead of by the design characteristics of the horn itself. The horn provides an additional element of directional control, and acts to block any side lobes that may be generated at the horn""s throat end by physical separation of the output ports of the driver manifolds.
In a further aspect of the invention, the length of each waveguide of the driver manifolds is relatively short in length in relation to the wavelength of the acoustical waves passing through the manifold at the highest frequency at which the horn loudspeaker system is intended to operate. Preferably, the manifold waveguides have acoustic path lengths no longer than approximately three wavelengths at the highest operating frequency. Suitably, for a horn loudspeaker system having upper frequency range of 15,000 Hz, the length of the manifold would be in the range of 3 inches. Manifolds substantially exceeding 3 inches in length would produce relatively long acoustical path lengths between the input port and aligned output ports of the manifold at high frequencies, resulting in increased distortion in the sound pressure wave as it passes through the waveguides. On the other hand, in manifolds substantially shorter than 3 inches in length, the bends in the waveguides used to equalize acoustical path lengths would increase to the point where the bends would produce excessive reflections within the manifold.
In still a further aspect of the invention, each of the manifold waveguides increases in cross-sectional area from the input port of the manifold to the output port of each waveguide. Such expansion acts to further reduce the distortion effects the waveguide has on the acoustic sound waves as they pass through the manifold.
The invention also involves a method for providing control over the dispersion characteristics of a horn loudspeaker which includes providing both a source of acoustic power and a loudspeaker horn with an elongated throat opening, dividing the acoustic power produced by the acoustic power source between at least two acoustical paths, and propagating the divided acoustic power along the at least two acoustical paths to two separate aligned outputs at the elongated throat opening of the horn so as to simulate a line array of acoustic power sources at the elongated throat opening.
Therefore, it is a primary object of the invention to provide a manifold for a loudspeaker horn and a method of driving a loudspeaker horn which permits tighter control over the dispersion characteristics of a horn loudspeaker system. It is another object of the invention to provide a horn loudspeaker system which can be readily arrayed without destructive interaction between the acoustic outputs of the loudspeakers. It is a further object of the invention to provide a horn loudspeaker system and method with the foregoing advantages which can minimize distortion. Yet Other objects of the invention will be apparent from the following description and claims.